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Method for reduction of random dopant induced threshold voltage variation

IP.com Disclosure Number: IPCOM000042241D
Publication Date: 2005-Feb-03
Document File: 4 page(s) / 21K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for reduction of random dopant induced threshold voltage variation. Benefits include improved functionality and improved performance.

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Method for reduction of random dopant induced threshold voltage variation

Disclosed is a method for reduction of random dopant induced threshold voltage variation. Benefits include improved functionality and improved performance.

Background

              Random variation of device parameters is important for circuit design. A random number and position of dopants in the channel of metal oxide semiconductor field-effect transistors (MOSFETs) can cause random variations in threshold voltages. Random dopant fluctuations (RDFs) are expected to get worse with device scaling and are not controlled with better process control.

              To reduce RDF in transistors, a retrograde well can be used on bulk MOS devices. However, with device scaling, this technique does not work due to finite dopant diffusion and a worse short-channel effect. Design solutions are possible. However, they tend to require larger transistors that impact silicon areas.

              A trigate device is considered to be a good candidate for future device scaling. It is a silicon-on-insulator (SOI) device with gates on three sides of the silicon (see Figure 1)

General description

              The disclosed method is for the reduction of random dopant induced threshold voltage variation. The method uses the RDF dependence on channel doping in combination with the suitable work function of a metal gate to reduce Vt fluctuation. A trigate device serves as an example of how the disclosed method can be applied.

              The key element of the disclosed method is to realize a doping in the body of the device that has the minimum RDF-induced Vt fluctuation. To obtain the required Vt and Ioff, a metal gate with a suitable work function should be used, such as a trigate device. The reduced RDF-induced Vt fluctuation improves performance and the area required for integrated circuits.

Advantages

              The disclosed method provides advantages, including:

•             Improved functionality due to controlling the threshold voltage and its RDF-induced variations independently

•             Improved performance due to minimizing transistor mismatch due to RDF and selecting the appropriate threshold voltage to maintain circuit functionality

 

Detailed description

              The disclosed method can be applied to a device that has a doping for which RDF is minimum. Three-dimensional (3-D) device simulations of RDF-induced Vt variation show that there exists a doping for which RDF is minimum (see Figure 2). The method exploits the presence of this minimum to make RDF-resistant devices.

              Using 3-D device simulations, the doping at which RDF is minimal can be identified. To meet the Ioff and Vt for the device, we can use a metal-gate (along with a dielectric with a high dielectr...